Preparation of antiplasticizers for thermoplastic polyesters

ABSTRACT

A process for making bis(aryloxyalkyl)terephthalates useful as antiplasticizers for thermoplastic polyesters is disclosed. Dimethyl terephthalate is reacted with an excess of an aryloxyalkanol in the presence of a condensation catalyst to produce an intermediate mixture comprising a bis(aryloxyalkyl)terephthalate, a mono(aryloxyalkyl)terephthalate, and unreacted aryloxyalkanol. This mixture continues to react at reduced pressure while unreacted aryloxyalkanol is removed and the mono-ester content is reduced to less than 1 mole % based on the combined amounts of mono- and bis-esters. Both steps are performed substantially in the absence of oxygen. Additional unreacted aryloxyalkanol is then removed to provide a purified bis(aryloxyalkyl)terephthalate having an overall purity of at least 98 mole % and a yellowness index less than 10. Careful control over catalysis, exposure to air, and other process conditions enables the preparation of high yields of bis(aryloxyalkyl)terephthalates that have low color and other valuable attributes. A method of producing bis(aryloxyalkyl)terephthalate articles having improved compressive strength is also disclosed.

FIELD OF THE INVENTION

The invention relates to antiplasticizer additives for polymers,especially thermoplastic polyesters, and in particular, to a process formaking bis(aryloxyalkyl)terephthalates having high purity and low color.

BACKGROUND OF THE INVENTION

Bis(aryloxyalkyl)terephthalates have been used to make adhesives,recording media, crystallization accelerators, and photosensitivelayers. Recently, their use as gas-barrier additives for thermoplasticpolyesters such as polyethylene terephthalate (PET) has been disclosed(see, e.g., U.S. Pat. Appl. Publ. Nos. 2010/0143546 and 2010/0143547).The additive functions as an antiplasticizer: it enhances modulus andtensile strength, thereby reducing creep when bottles are stacked.Additionally, it reduces the permeability of PET to carbon dioxide andoxygen, which improves the shelf life of carbonated beverages,particularly for smaller bottle sizes, and oxygen-sensitive drinks suchas juice, tea products, or beer (see also U.S. Pat. Appl. Publ. No.2006/0275568). As demonstrated in the '546 publication, adding just 3wt. % of bis(2-phenoxyethyl)terephthalate increased barrier improvementfactor by almost 20% and added about two weeks to shelf life. Theprocess for making the bis(aryloxyalkyl)terephthalate is not discussed.

In a typical laboratory setting, bis(aryloxyalkyl)terephthalates aremade by reacting terephthaloyl chloride with the correspondingaryloxyalkanol. For example, the reaction of terephthaloyl chloride with2-phenoxyethanol in the presence of excess triethylamine and a solvent,followed by an organic workup to remove the ammonium salt,concentration, and recrystallization providesbis(2-phenoxyethyl)-terephthalate (see Scheme 1, compound 2 andSynthetic Examples 1 and 2 in U.S. Pat. Appl. Publ. No. 2009/0087764).Unfortunately, the lab procedure is impractical on a commercial scalebecause of the cost of terephthaloyl chloride and, among other issues,the need to recover a solvent and dispose of the ammonium salt.

In another laboratory approach (U.S. Pat. No. 3,557,167, Example 13),bis(2-phenoxyethyl)terephthalate is prepared by reacting diphenylterephthalate with ethylene carbonate (1:3 molar ratio) in the presenceof lithium chloride, followed by recrystallization from benzene.Limiting commercial use here are the need to synthesize diphenylterephthalate (usually from terephthaloyl chloride), the relatively highcost of ethylene carbonate, and material losses when carbon dioxide iseliminated as a by-product.

Direct esterification of alcohols with terephthalic acid (TA) offershope of a simpler purification by taking advantage of an acidic startingmaterial and a neutral product. However, temperatures in excess of 250°C. (see, e.g., U.S. Pat. No. 4,737,569 or WO 82/00289) are normallyrequired, and the potential ease-of-isolation advantages are underminedby the relatively poor solubility of TA compared with that of dimethylterephthalate (DMT). Based on our own work, the approach may also impartunacceptably high color when the aryloxyalkanol is reacted with TA.

In one approach to making bis(aryloxyalkyl)terephthalates, thearyloxyalkanol is reacted with dimethyl terephthalate in the presence ofa transesterification catalyst. Because the reaction is equilibriumcontrolled, it is difficult to convert substantially all of the DMT to abis-ester, and the product can contain too muchmono(aryloxyalkyl)terephthalate. An excess of the aryloxyalkanol can beused to shift the equilibrium toward completion. Unfortunately, sidereactions can complicate this process, resulting in discoloration of theproduct. For a clear plastic bottle application, however, low color isimportant.

Additional problems result from the use of certain traditionalcondensation catalysts for the esterification. In particular, ifresidues from catalysts containing cobalt, manganese, cadmium,magnesium, and other metals are not avoided or thoroughly removed fromthe bis(aryloxyalkyl)terephthalates, they can cause an undesirablereduction in the molecular weight and intrinsic viscosity of the PETplastic into which the antiplasticizer is formulated, resulting ininferior blow-molded bottles (see U.S. Pat. Appl. Publ. No.2006/0275568).

Some processes give low conversion to the desired bis-ester, whileothers generate the desired product, but in low yield or with too highan acid number, hydroxyl number, or moisture content. However, all ofthese considerations can be important when thebis(aryloxyalkyl)terephthalate is destined for making blow-molded PETbottles.

Yet another consideration is how easily the antiplasticizer can beprocessed uniformly with thermoplastics. Certainbis(aryloxyalkyl)terephthalates tend to be rather brittle, especiallywhen produced at high purity and crystallinity. However, theantiplasticizer, when converted to pellets, prills, pastilles, flakes,granules or other articles, needs adequate crush strength so that it canbe shipped or stored in gaylords, rail cars, tank trucks, or the likewithout disintegrating and forming dust. Moreover, when theantiplasticizer articles are combined with pellets of the thermoplasticpolyester (e.g., PET), they should remain capable of shipping andstorage without forming dust or separating from the dry-blended mixture.

In sum, bis(aryloxyalkyl)terephthalates are valuable antiplasticizersfor thermoplastic polymers, especially PET, but a viable commercialsynthesis is still needed. A suitable process would avoid pitfalls of alaboratory-scale process such as expensive starting materials, use of asolvent, and isolation/disposal of an ammonium salt. Preferably, theprocess would allow recycle and reuse of reactants and could bepracticed using conventional esterification equipment and techniques.The process should avoid catalysts that reduce PET molecular weightduring formulation into blow-molded articles. A valuable process wouldprovide high yields of bis(aryloxyalkyl)terephthalates having the lowcolor, low acid number, and low hydroxyl number needed to make theproduct acceptable for use as an antiplasticizer in the production ofblow-molded thermoplastics. Ideally, the antiplasticizer could beformulated in a way that enables it to be stored and shipped withoutdisintegrating, thereby ensuring an even distribution when it iscombined and melt processed with thermoplastic polymers.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to a process for makingbis(aryloxyalkyl)terephthalates suitable for use as antiplasticizers forthermoplastic polyesters. The process comprises three steps. First,dimethyl terephthalate reacts with an excess of an aryloxyalkanol in thepresence of a condensation catalyst comprising a Group 3, 4, 12, 13, 14,or 15 metal at a temperature less than the boiling point of thearyloxyalkanol to produce an intermediate mixture. The intermediatemixture comprises a bis(aryloxyalkyl)terephthalate, amono(aryloxy-alkyl)terephthalate, and unreacted aryloxyalkanol.

In a second step, the intermediate mixture continues to react at atemperature within the range of 180° C. to 250° C. under reducedpressure while unreacted aryloxyalkanol is removed. During this step,the mono(aryloxyalkyl)terephthalate content of the mixture is reduced toless than 1 mole % based on the combined amounts of mono- andbis-esters. At least the first two steps are performed substantially inthe absence of oxygen.

In a third step, additional unreacted aryloxyalkanol is removed toprovide a purified bis(aryloxyalkyl)terephthalate having an overallpurity of at least 98 mole % and a yellowness index less than 10. Wesurprisingly found that careful control over catalysis, exposure tooxygen, and other process conditions are needed for making high yieldsof low-color bis(aryloxyalkyl)terephthalates that are valuableantiplasticizers for thermoplastic polymers.

In another aspect, the invention relates to a method of producingantiplasticizer articles. The method comprises melt blending abis(aryloxy-alkyl)terephthalate with polyethylene terephthalate (PET) togive a polymer blend, and then forming antiplasticizer articles from thepolymer blend. In this method, from 1 to 50 wt. % of PET is used basedon the amount of polymer blend. The compressive strength of the articlesis at least 25% greater than that of similar articles made from only thebis(aryloxyalkyl)terephthalate. The method provides articles thatmaintain their integrity during storage or shipping.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the invention relates to a process for making abis(aryloxyalkyl)terephthalate suitable for use as an antiplasticizerfor a thermoplastic polyester.

Esterification

In a first step (a), dimethyl terephthalate reacts with an excess of anaryloxyalkanol in the presence of a particular condensation catalyst ata temperature less than the boiling point of the aryloxyalkanol (i.e.,at 760 mm Hg) to produce an intermediate mixture comprising abis(aryloxyalkyl)terephthalate, a mono(aryloxy-alkyl)terephthalate, andunreacted aryloxyalkanol.

Dimethyl terephthalate (DMT) is commercially available. DMT suitable foruse in the process can come from any desired source. Because DMT isoften synthesized from terephthalic acid (TA) or other TA derivatives,the most economical source of DMT may contain a low concentration of TA.We found with a spiking experiment (addition of 1 mol % TA to DMT) thatDMT containing a substantial amount of TA performs well in the inventiveprocess. Thus, the purity level of the DMT used is not consideredcritical. In particular, DMT containing up to 10 wt. % of TA is believedto be suitable for use in the process.

The DMT is reacted with an aryloxyalkanol. Suitable aryloxyalkanols havean aryloxy group, a divalent alkylene group, and a hydroxyl group. Thearyloxy group has at least one benzene ring that is attached directly toan oxygen atom, and this oxygen atom is bonded to the divalent alkylenegroup. The aryloxy group can be substituted with alkyl, aryl, fusedaryl, heterocyclyl, halogen, nitro, or other groups that do notinterfere with the esterification reaction. Preferably, the aryloxygroup is phenoxy or alkyl-substituted phenoxy. Most preferably, thearyloxy group is phenoxy. The divalent alkylene group links the aryloxygroup to the hydroxyl group. It is linear, branched, or cyclic andpreferably contains from 2 to 8 carbons, more preferably from 2 to 4carbons. Thus, suitable aryloxyalkanols include, e.g., 2-phenoxyethanol,2-(4-methylphenoxy)ethanol, 2-(4-chlorophenoxy)ethanol,2-phenoxy-2-propanol, 4-phenoxycyclohexanol, and the like, and mixturesthereof. 2-Phenoxyethanol is most preferred.

Preferably, the aryloxyalkanol has a boiling point at atmosphericpressure greater than 210° C. Ideally, the aryloxyalkanol remains in thereaction mixture during esterification without the need for expensivepressurization.

An excess of the aryloxyalkanol is used. By “excess” we mean that enougharyloxyalkanol is used to react with substantially all of the dimethylterephthalate present. Preferably, from 1.9 to 3.0, more preferably from2.0 to 2.8, molar equivalents of the aryloxyalkanol are reacted withDMT. Along with removal of methanol, which forms as a by-product ofesterification, use of an excess of the aryloxyalkanol helps to shiftthe equilibrium-controlled reaction in favor of thebis(aryloxyalkyl)terephthalate product.

A condensation catalyst is used to react DMT and the aryloxyalkanol.Suitable condensation catalysts are those capable of transesterifyingDMT with the aryloxyalkanol to give a bis(aryloxyalkyl)terephthalate.While many kinds of catalysts will promote esterification, the catalystused in the inventive process also cannot interfere with subsequentprocessing of the thermoplastic polyester into which thebis(aryloxyalkyl)terephthalate is added. It is known that certainelements, if present in the additive as catalyst residues, can reducethe molecular weight or intrinsic viscosity of the thermoplasticpolyester when the polyester is melt processed (c.f., U.S. Pat. Appl.Publ. Nos. 2006/0275568 and 2010/0143546).

Thus, suitable condensation catalysts for use in the inventive processcomprise a Group 3, 4, 12, 13, 14, or 15 metal, more preferably a Group4 or 13 metal, and most preferably a Group 4 metal. Suitable catalystscomprise yttrium, lanthanum, titanium, zirconium, aluminum, gallium,germanium, antimony, tin, or zinc. More preferred catalysts comprisetitanium or aluminum. Suitable catalysts include, for example, metaloxides, alkoxides, and carboxylates. Specific examples includetetra(ethoxy)titanium, tetra(n-propoxy)titanium,tetra(isopropoxy)titanium tetra(n-butoxy)titanium,tetra(isobutoxy)titanium, tetra(2-ethylhexoxy)titanium,tetra(n-butoxy)zirconium, tri(n-butoxy)aluminum, aluminum triacetate,germanium(IV) oxide, dibutyltin oxide, dibutyltin dilaurate, dibutyltindiacetate, and the like. Organotitanate catalysts, particularlytetra(alkoxy)titanium catalysts such as Tyzor® tetra(n-butoxy)titanium,a product of DuPont, are particularly preferred. Suitable catalysts arealso available from Johnson-Matthey as Vertec® organic titanates.

In a preferred aspect, the catalyst is not moisture-sensitive. Suitablecatalysts in this regard comprise a Group 12 metal, such as zinccarboxylates, particularly zinc acetate. Selection of such a catalystobviates the need, on occasion, to remove moisture from the reactantmixture prior to charging the catalyst. Compare Example 5, below (zincacetate catalyst is charged with water) with Example 1 (moisture isremoved prior to charging a tetra(alkoxy)titanium catalyst).

The amount of condensation catalyst needed depends on the particularcatalyst used, the particular aryloxyalkanol, the reaction conditions,scale, and other factors and is within the skilled person's discretion.Typically, the amount will be within the range of 1 to 1000 ppm,preferably from 10 to 500 ppm, based on the total amount of DMT andaryloxyalkanol used.

The esterification reaction is performed at a temperature less than theboiling point of the aryloxyalkanol. This prevents the aryloxyalkanolfrom being removed before it can react with the DMT. Preferably, thetemperature is within the range of 100° C. to 250° C., more preferablyfrom 130° C. to 230° C., most preferably from 150° C. to 220° C.

Surprisingly, we found that the bis(aryloxyalkyl)terephthalate can bemade at relatively high temperature (e.g., 220° C.) without developingan unacceptable level of yellowness if oxygen is carefully excluded fromthe reaction mixture (see Example 1, below). Conversely, if oxygen isintentionally introduced, color development is rapid and significant(Comparative Examples 2 and 6A-6E). In general, if oxygen is notcarefully excluded during esterification and subsequent removal of thearyloxyalkanol (i.e., during the first and second steps), thebis(aryloxyalkyl)-terephthalate can have a yellowness index that isunacceptably high for use in thermoplastic polyesters intended forblow-molded bottles.

As used herein, “substantially in the absence of oxygen” means that duecare is exercised to minimize or eliminate opportunities foroxygen-containing gases, especially air, to come into contact withheated reaction mixtures during either of the first two steps of theclaimed process. Thus, the reaction should be performed under anatmosphere of nitrogen, argon, or other inert or oxygen-free gas. When apartial vacuum is used during initial stripping, inert gas rather thanair should be bled into the reactor. Other sources of air can includepoor stirrer bearing seals, poorly sealed fittings, or the like. Theskilled person will be aware of other possible sources of air leaks,which will depend largely on the particular equipment chosen forperforming the first and second steps.

Optionally, the esterification is performed in the presence of anantioxidant. Suitable antioxidants include phenolic antioxidants,organophosphorus compounds, lactones, or the like. Many antioxidants arecommercially available from BASF and other suppliers. For examples ofsuitable antioxidants, see U.S. Pat. Appl. Publ. No. 2010/0233405, theteachings of which are incorporated herein by reference, and referencescited therein.

The intermediate mixture resulting from initial reaction step (a)comprises a bis(aryloxyalkyl)terephthalate, amono(aryloxyalkyl)terephthalate, and unreacted aryloxyalkanol. Normally,the mixture also includes methanol, which is eliminated in theesterification. Preferably, at least 90%, more preferably at least 95%,of the dimethyl terephthalate reacts in the initial reaction step. It isnot necessary, however, that all of the DMT be converted to thebis(aryloxyalkyl)terephthalate (also called “bis-ester”) at this stage.Normally, a substantial proportion of themono(aryloxyalkyl)terephthalate (“mono-ester” or “half ester”) remains.Preferably, from 65 to 85 mole %, more preferably from 70 to 80 mole %,of the dimethyl terephthalate is converted to thebis(aryloxyalkyl)terephthalate, with most of the balance (typically 15to 35 mole %) being converted to the mono-ester. While it is tempting topush conversion to the bis-ester to a high level during the initialreaction step, milder conditions, including lower temperature, may helpto ensure an acceptably low color in the intermediate mixture andpurified bis(aryloxyalkyl)-terephthalate.

Continued Esterification with Aryloxyalkanol Removal

In a second step (b), reaction of the intermediate mixture continues ata temperature within the range of 180° C. to 250° C. while unreactedaryloxyalkanol is removed under reduced pressure. During this step, themono(aryloxyalkyl)-terephthalate content of the mixture is reduced toless than 1 mole % based on the combined amounts of mono- andbis-esters.

As in the first step, temperature control in the second step is notcritical for isolating a purified bis(aryloxyalkyl)terephthalate havinga desirably low yellowness index provided that oxygen is carefullyexcluded. Thus, this second process step is also performed substantiallyin the absence of oxygen. Preferably, the temperature for this step iswithin the range of 150° C. to 250° C., more preferably from 175° C. to230° C., and most preferably from 185° C. to 220° C.

As noted earlier, the aryloxyalkanol is used in excess in theesterification reaction. Thus, unreacted aryloxyalkanol needs to beremoved from the intermediate mixture. This removal is accomplished byheating under reduced pressure. Preferably, a gentle vacuum (e.g.,700-550 mm Hg) is applied, which assists in removal of mostly methanol.Usually, the vacuum is gradually improved (e.g., from 550 mm to 20 mmHg), typically at or near the desired maximum temperature, to removemost of the aryloxyalkanol. The pressure can be further reduced ifdesired to remove a greater proportion of the unreacted aryloxyalkanol.

Heating under vacuum in step (b) removes much of the aryloxyalkanol fromthe intermediate mixture. Coincidentally, most of themono(aryloxyalkyl)-terephthalate present after the initialesterification reacts with aryloxyalkanol and is converted to thedesired bis-ester. Thus, the reaction is continued until themono(aryloxyalkyl)terephthalate content of the mixture is reduced toless than 1 mole %, preferably less than 0.5 mole %, based on thecombined amounts of mono- and bis-esters.

It is often helpful to include an inert gas purge along with heating andvacuum to assist in removal of unreacted aryloxyalkanol. The inert gascan be nitrogen, argon, or the like. As noted above, oxygen-containinggases such as air are excluded during this step. Typically, the flow ofinert gas is adjusted to achieve the desired reduction in pressure.Thus, if vacuum is improved, a corresponding decrease in the amount ofinert gas purge will be applied. The unreacted aryloxyalkanol isvaluable and is, of course, preferably recovered and reused.

Additional Removal of Aryloxyalkanol

In a third step (c), additional unreacted aryloxyalkanol is removed toprovide a purified bis(aryloxyalkyl)terephthalate having an overallpurity of at least 98 mole % and a yellowness index less than 10.

This step is used to reduce the aryloxyalkanol content of thebis(aryloxyalkyl)-terephthalate to a level that is acceptable forantiplasticizer applications. Typically, thebis(aryloxyalkyl)terephthalate, following completion of step (b), willcontain up to 5 mole % of residual aryloxyalkanol. For commercial use,however, the bis(aryloxyalkyl)terephthalate needs to have an overallpurity of at least 98 mole percent. Preferably, it also contains lessthan 1 mole %, more preferably less than 0.5 mole %, and most preferablyless than 0.25 mole % of the aryloxyalkanol.

In one suitable approach, in-situ stripping of the product from step (b)under vacuum, preferably with an inert gas purge, is used to furtherreduce the aryloxyalkanol content. It remains important to perform anelevated temperature strip substantially in the absence of oxygen.Temperature is preferably within the range of 130° C. to 230° C., mostpreferably from 150° C. to 210° C. Typically, the pressure is reduced tobelow 20 mm Hg for this step, preferably to below 10 mm Hg.

In another suitable approach, the product is removed from theesterification reactor and is subjected to vapor (methanol, water, etc.)and/or inert gas stripping, wiped-film evaporation, steam stripping,fractional melt crystallization, solvent crystallization, or othersimilar techniques until the aryloxyalkanol content has been reduced toan acceptable level. Methods that permit recovery and reuse of thearyloxyalkanol are preferred.

Purified bis(aryloxyalkyl)terephthalate

The purified bis(aryloxyalkyl)terephthalate has a yellowness index lessthan 10. This is the maximum tolerable yellowness index for the targetedapplication in blow-molded articles, particularly blow-molded PETbottles. Preferably, the yellowness index is less than 5, and morepreferably it is less than 2. Numerous factors—some known, someunknown—contribute to the development of yellow color in thebis(aryloxyalkyl)terephthalate.

Yellowness index is normally measured using a color spectrophotometer. Asuitable technique is described in more detail in the experimentalsection below. Powder samples can be analyzed using an instrument suchas a ColorQuest XE spectrophotometer, which is available from HunterLab.Samples are conveniently prepared by pulverizing a purifiedbis(aryloxyalkyl)terephthalate sample to a fine powder, spreading thesample to form a relatively uniform layer, and analyzing as describedbelow. A standard method (ASTM E313-10) is used to calculate yellownessindex.

For applications that demand a bis(aryloxyalkyl)terephthalate havingexceptionally low yellowness index (e.g., less than 5), it may behelpful to treat the purified material with an adsorbent to furtherreduce its yellowness index. Suitable adsorbents include Magnesol®adsorbent (magnesium silicate, product of Dallas Group of America),activated carbons or charcoal, diatomaceous earth, aluminas, clays,silicas, titanias, magnesias, and the like, or combinations thereof. Wefound that, on a weight basis, Magnesol adsorbent is particularlyeffective in reducing yellowness index in a purifiedbis(aryloxyalkyl)terephthalate. See Examples 3F-3H below, where aslittle as 1 wt. % Magnesol adsorbent reduced yellowness index from about8 to less than 2.

In addition to yellowness index, the purifiedbis(aryloxyalkyl)terephthalate preferably meets other specificationsthat may be important depending on the targeted application. Forinstance, the hydroxyl number of the bis(aryloxyalkyl)terephthalate ispreferably less than that of the thermoplastic polyester with which itis to be combined. More preferably, the hydroxyl number is less than 1mg KOH/g, most preferably less than 0.5 mg KOH/g. The acid number canalso be important. Preferably, the acid number of the purifiedbis(aryloxyalkyl)terephthalate is less than that of the thermoplasticpolyester with which it is to be combined. More preferably, the acidnumber is less than 1 mg KOH/g, most preferably less than 0.5 mg KOH/g.If either the hydroxyl number or the acid number is too high, there maybe an undesirable impact on how the thermoplastic polyester (into whichthe antiplasticizer is formulated) processes.

The purified bis(aryloxyalkyl)terephthalate has an overall purity of atleast 98 mole %, preferably at least 99 mole %, and most preferably atleast 99.5 mole %. Thus, the total amount of DMT, aryloxyalkanol, andmono-ester present in the purified bis(aryloxyalkyl)terephthalate willnot exceed 2 mole %, and preferably will not exceed 1 mole %. Anyconvenient method of determining overall purity can be used, such asliquid chromatography, gel permeation chromatography, mass spectrometry,infrared spectroscopy, ¹H or ¹³C NMR spectroscopy, or the like, orcombinations of these techniques.

In a preferred aspect, the aryloxyalkanol is 2-phenoxyethanol, and theresulting bis(aryloxyalkyl)terephthalate isbis(2-phenoxyethyl)terephthalate, also known as “PEM.” PEM has proved tobe a valuable antiplasticizer additive for thermoplastic polyesters,particularly PET. As shown in U.S. Pat. Appl. Publ. No. 2010/0143546,the teachings of which are incorporated herein by reference, adding just3 wt. % of PEM into a PET formulation can increase barrier improvementsignificantly and add weeks to bottle shelf life.

The purified bis(aryloxyalkyl)terephthalate is preferably converted intoa form that facilitates its combination and blending with athermoplastic polyester. The post-manufacture treatment may comprisepelletizing, flaking, granulating, pastillating, prilling, spray drying,or other well-known techniques. The bis(aryloxyalkyl)terephthalate canbe converted either in pure form or as masterbatch with a portion of thethermoplastic polyester into which it will ultimately be compounded. Ifdesired, fillers or other additives can be included in the purifiedbis(aryloxyalkyl)terephthalate to make it more suitable for shipping orhandling for a particular use.

Method of Producing Antiplasticizer Articles

The invention includes a method of producing antiplasticizer articles.In this method, a bis(aryloxyalkyl)terephthalate is first melt blendedwith polyethylene terephthalate (PET) to give a polymer blend. Anydesired means can be used to melt blend the PET andbis(aryloxyalkyl)terephthalate. Antiplasticizer articles are then formedfrom the polymer blend. Techniques used to form the articles are wellknown, and include pelletizing, pastillating, prilling, flaking,granulating, and the like. The amount of PET used is from 1 to 50 wt. %,more preferably from 5 to 25 wt. %, most preferably from 10 to 25%,based on the amount of polymer blend.

We surprisingly found that such articles (typically in the form ofpellets, flakes, granules, pastilles, prills, or tablets) have acompressive strength as measured by ASTM D-1621, that is at least 25%greater than that of similar articles made from only thebis(aryloxyalkyl)terephthalate (see Example 8 and Comparative Example9). The bis(aryloxyalkyl)-terephthalates, when produced at high purity,can be brittle and prone to disintegration during storage or shipping.On the other hand, the articles require integrity if they are to beformulated effectively with other thermoplastic materials, such as PETpellets. The inventive method affords bis(aryloxyalkyl)-terephthalateantiplasticizers that meet this requirement. Because of their improvedcompressive strength, the antiplasticizers can be stored and shipped ingaylords, rail cars, tank trucks, or the like with minimaldisintegration and dust formation. Moreover, when the antiplasticizerarticles are combined with pellets of the thermoplastic polyester (e.g.,PET), they can be shipped, stored, and processed without forming dust orseparating from the dry-blended mixture. This ensures theantiplasticizer will be evenly distributed when the mixture is meltprocessed.

The following examples merely illustrate the invention. Those skilled inthe art will recognize many variations that are within the spirit of theinvention and scope of the claims.

Yellowness Index

A ColorQuest XE spectrophotometer (HunterLab) is used to analyze powdersamples of PEM to determine a yellowness index.

Sample preparation: A solid sample (10-15 g) of PEM is ground in aporcelain mortar for 2 min. and transferred to a 60×15 mm petri dish,which is tapped gently on the lab countertop three times to evenlydistribute the powder.

Instrument conditions: Mode: reflectance specular included (RSIN);aperture: 1.00 in.; UV filter position: normal; illuminant: D65/10. Eachsample is scanned in three different locations, and the data isaveraged.

Calculation of yellowness index: by ASTM E313-10.

EXAMPLE 1 Preparation of Bis(2-phenoxyethyl)terephthalate (“PEM”)

A 5-L round-bottom flask equipped with overhead stirrer, thermocouple,and nitrogen sparge tube is connected to an ice-water cooled vacuumcondenser and receiver flask. The reactor is charged with dimethylterephthalate, “DMT” (874 g, 4.5 mol, from Alfa Aesar) and2-phenoxyethanol, “2-PE” (1679 g, 12.2 mol, product of Dow Chemical).The reactor is heated to 110° C. to 120° C. to dissolve the DMT in the2-PE. The stirrer is set for 200 rpm, and the reaction mixture is heldat 110° C. to 120° C. for 15-30 min. under a nitrogen sparge (140mL/min) to remove moisture. Tyzor® tetra(n-butoxy)titanium catalyst(0.73 g, ˜300 ppm based on total reactants, product of DuPont) is addedto the reactor, and the contents are heated to 140° C. Distillate,predominantly methanol, is collected as the temperature is slowlyincreased in steps to 220° C. Thereafter, a gentle vacuum is applied.The pressure is slowly reduced (to 10 mm Hg) with a concurrent reductionin nitrogen sparging, and additional distillate, predominantly2-phenoxyethanol, is collected. The product, clear with a yellow tint,is cooled and recovered to give crystals with a slight cream color. Atthis point, further purification may be used to remove additional 2-PEand other impurities.

Gas chromatography analysis of the PEM product: 98.9% PEM, 0.0% DMT,0.1% mono(2-phenoxyethyl)terephthalate, 1.0% 2-PE. Yellowness index:1.01; acid number (by titration in acetone to a phenolphthaleinendpoint): 0.02 mg KOH/g.

COMPARATIVE EXAMPLE 2

The procedure of Example 1 is generally repeated, except that an airleak is introduced that prevents the vacuum from being lowered below 45mm Hg.

Yellowness index: 8.93; acid number: 0.03 mg KOH/g.

EXAMPLES 3A-3H Effect of Adsorbents on Yellowness Index

PEM having a relatively high color (yellowness index=8.4) is treatedwith various adsorbents in an attempt to remove color. Thus, eight 4-oz.jars, each containing PEM (50 g), are placed in an oven at 130° C. tomelt. A second set of jars containing Magnesol® D60 adsorbent (magnesiumsilicate, product of Dallas Group of America), carbon black (Nuchar),and diatomaceous earth (Fisher Scientific) are also placed in the oven.Glass powder funnels containing a folded cone of Whatman 42 filter paperare placed on top of Erlenmeyer flasks, and these are also put into theoven. Once the PEM samples have melted, the adsorbents are added to thePEM and swirled 30 seconds to ensure good mixing. The samples are thenfiltered. About 15 g of PEM filters through over 45 minutes. Thefiltrates are analyzed for color and acid number. Results appear inTable 1.

The results demonstrate that PEM color can be further reduced usingadsorbents. Diatomaceous earth is generally ineffective. Based on theamounts of adsorbent needed to achieve a desirably low color, Magnesoloutperforms carbon black, giving PEM of very low color even with only 1wt. % adsorbent.

TABLE 1 Effect of Adsorbents on Yellowness Index Ex. Adsorbent (wt. %)Acid # (mg KOH/g) Yellowness index 3A None (control) 0.09 8.36 3BDiatomaceous earth (10%) 0.08 5.89 3C Carbon black (1%) 0.12 4.49 3DCarbon black (5%) 0.09 2.18 3E Carbon black (10%) 0.08 1.07 3F Magnesol(1%) 0.07 1.48 3G Magnesol (5%) 0.06 1.13 3H Magnesol (10%) 0.09 1.16

EXAMPLE 4 Effect of Added Terephthalic Acid

The procedure of Example 1 is generally followed, except that 1.0 mol %of terephthalic acid, based on the amount of DMT charged, is included inthe reactor charge. Yellowness index: 1.47; acid number: 0.00 mg KOH/g.

The example demonstrates TA is esterified in the process, and thatmixtures of DMT and TA can be used to manufacture PEM having acceptableproperties for use as an antiplasticizer.

EXAMPLE 5 Zinc Acetate as a Catalyst in a High-Moisture Esterification

The procedure of Example 1 is generally followed to make PEM with theadjustments indicated. First, zinc acetate (1.35 g) replacestetra(n-butoxy)titanium as the catalyst. The initial reactor chargeincludes the zinc acetate and deionized water (122 g). (Zinc acetate iscompatible with water, while the titanium catalyst is not.) The maximumtemperature is 200° C. The product is slightly cloudy, but yields verywhite crystals with an acid number of 0.03 mg KOH/g.

The example demonstrates that a high moisture content in the reactionmixture can be tolerated well if a condensation catalyst comprising aGroup 12 metal is selected. This obviates the need to remove traces ofmoisture from the reactants before charging the catalyst.

COMPARATIVE EXAMPLES 6A-6E Air Sparging

A slight vacuum is applied to a reactor containing molten PEM at 195° C.so that it pulls a small stream of air through a metal dip tube and intothe PEM. Samples of PEM are periodically removed from the reactor andimmediately cooled before being analyzed for yellowness index.

TABLE 2 Effect of Air Sparging on Yellowness Index Ex. Total sparge time(min.) Yellowness index 6A 0 6.12 6B 20 11.23 6C 40 13.11 6D 60 14.49 6E120 16.49

Comparative Examples 6A-6E demonstrate the importance of excludingoxygen, especially in the early portion of the experiment, for makingPEM having low color.

EXAMPLE 7 Preparation of a Melt Blend of PET in PEM

Bis(2-phenoxyethyl)terephthalate (“PEM,” 100 g) is heated with stirringat 190° C. until molten. Bottle-grade polyethylene terephthalate (PET, 5g) is added, and the temperature is gradually increased until the PETbecomes soluble (about 225° C.). Additional PET is added in 5-gincrements to the stirred mixture at 230° C. over several hours. Somedarkening occurs during the course of the additions, and a total of 30 gof PET (23.1 wt. % based on the combined amount of PET+PEM) is added.The final product is transferred to a Teflon dish, and it cools to forman off-white cake. The polymer blend is less friable and morebreakage-resistant than pure PEM.

EXAMPLE 8 Pellets from a 20 wt. % PET in PEM Blend

PEM (169.3 g) is heated in a 500-mL flask equipped with a thermocouple,mechanical stirrer, and nitrogen atmosphere. When the temperaturereaches 230° C., bottle-grade polyethylene terephthalate (PET, 42.3 g)is added to the molten PEM in three portions while allowing each portionto dissolve before adding the next. After about 1.5 h, all of the PEThas dissolved to provide a blend containing 20 wt. % PET. The resultingblend is poured into 1″-diameter, flat-bottom scintillation vials tohalf-fill each vial. The vials are allowed to cool overnight. Each vialis scored with a diamond-tipped pen and carefully fractured with a smallhammer to recover the resulting polymer “pellet.” The top surface ofeach pellet is removed by abrasion with 80-grit sandpaper to provide aflat surface. The pellets, which average 0.98″ in diameter and 0.73″tall, are submitted for physical testing. Compressive strength (avg., byASTM D-1621): 453 psi. Friability (avg. weight loss, by tumbling, ASTMC-421): 47%.

COMPARATIVE EXAMPLE 9

The procedure of Example 8 is generally followed except that PET isomitted. Thus, PEM is simply heated until molten and transferred to thescintillation vials to form pellets. Compressive strength (avg.): 153psi. Friability (avg. wt. loss): 96%.

Example 8 and Comparative Example 9 demonstrate the improved compressivestrength and friability of PEM compositions that incorporate PET. Theresults suggest that pellets, pastilles, tablets, or other articles ofPEM formulated to contain up to 20 wt. % PET will have advantagescompared with PEM alone for shipping, storage, and formulation into PET.

The preceding examples are meant only as illustrations; the followingclaims define the invention.

1. A process for making a bis(aryloxyalkyl)terephthalate suitable foruse as an antiplasticizer for polymers, comprising the steps of: (a)reacting dimethyl terephthalate with 1.9 to 3.0 molar equivalents of anaryloxyalkanol in the presence of a condensation catalyst comprising aGroup 3, 4, 12, 13, or 15 metal at a temperature less than the boilingpoint of the aryloxyalkanol to produce an intermediate mixturecomprising a bis(aryloxyalkyl)terephthalate, amono(aryloxyalkyl)terephthalate, and unreacted aryloxyalkanol; (b)continuing to react the intermediate mixture at a temperature within therange of 150° C. to 250° C. under reduced pressure while removingunreacted aryloxyalkanol and reducing themono(aryloxyalkyl)terephthalate content of the mixture to less than 1mole % based on the combined amounts of mono- and bis-esters; and (c)removing additional unreacted aryloxyalkanol to provide a purifiedbis(aryloxyalkyl)terephthalate having an overall purity of at least 98mole % and a yellowness index less than 10; wherein at least steps (a)and (b) are performed substantially in the absence of oxygen.
 2. Theprocess of claim 1 wherein the aryloxyalkanol has a boiling point atatmospheric pressure greater than 210° C.
 3. The process of claim 1wherein the aryloxyalkanol is 2-phenoxyethanol and thebis(aryloxyalkyl)terephthalate is bis(2-phenoxyethyl)terephthalate(PEM).
 4. The process of claim 1 wherein from 2.0 to 2.8 molarequivalents of the aryloxyalkanol are used in step (a).
 5. The processof claim 1 wherein from 70 to 80 mole % of the dimethyl terephthalate isconverted to the bis(aryloxyalkyl)terephthalate in step (a).
 6. Theprocess of claim 1 wherein the catalyst comprises titanium or zirconium.7. The process of claim 1 wherein the catalyst comprises zinc.
 8. Theprocess of claim 1 wherein the purified bis(aryloxyalkyl)terephthalatehas a yellowness index less than
 5. 9. The process of claim 1 whereinthe purified bis(aryloxyalkyl)terephthalate has an overall purity of atleast 99 mole %.
 10. The process of claim 1 wherein the unreactedaryloxyalkanol is removed in step (b) with a gas or vapor purge.
 11. Theprocess of claim 1 wherein step (b) is performed at a temperature withinthe range of 175° C. to 230° C.
 12. The process of claim 1 wherein theunreacted aryloxyalkanol is removed in step (c) under reduced pressurewith a gas or vapor purge.
 13. The process of claim 1 wherein theunreacted aryloxyalkanol is removed in step (c) by fractional melt orsolvent crystallization.
 14. The process of claim 1 further comprisingpelletizing, flaking, granulating, pastillating, prilling, or spraydrying the purified bis(aryloxyalkyl)terephthalate.
 15. The process ofclaim 14 performed in the presence of PET.
 16. The process of claim 1wherein the purified bis(aryloxyalkyl)terephthalate is treated with anadsorbent to further reduce its yellowness index.
 17. The process ofclaim 16 wherein the adsorbent is magnesium silicate.
 18. Abis(aryloxyalkyl)terephthalate made by the process of claim
 1. 19. Amethod of producing antiplasticizer articles, comprising: (a) meltblending a bis(aryloxyalkyl)terephthalate with polyethyleneterephthalate (PET) to give a polymer blend, and (b) formingantiplasticizer articles from the polymer blend; wherein from 1 to 50wt.% of PET is used based on the amount of polymer blend; and whereinthe compressive strength by ASTM D-1621 of the articles formed in step(b) is at least 25% greater than that of similar articles made from onlythe bis(aryloxyal kyl)terephthalate.
 20. The method of claim 19 whereinthe articles are in the form of pellets, flakes, granules, pastilles,prills, or tablets.
 21. A process for making abis(aryloxyalkyl)terephthalate suitable for use as an antiplasticizerfor polymers, comprising the steps of: (a) reacting dimethylterephthalate with an excess of an aryloxyalkanol in the presence of acondensation catalyst comprising a Group 3, 4, 12, 13, 14, or 15 metalat a temperature less than the boiling point of the aryloxyalkanol toproduce an intermediate mixture comprising abis(aryloxyalkyl)terephthalate, a mono(aryloxyalkyl)terephthalate, andunreacted aryloxyalkanol; (b) continuing to react the intermediatemixture at a temperature within the range of 150° C. to 250° C. underreduced pressure while removing unreacted aryloxyalkanol and reducingthe mono(aryloxyalkyl)terephthalate content of the mixture to less than1 mole % based on the combined amounts of mono- and bis-esters; (c)removing additional unreacted aryloxyalkanol to provide a purifiedbis(aryloxyalkyl)terephthalate having an overall purity of at least 98mole % and a yellowness index less than 10; and (d) treating thepurified bis(aryloxyalkyl)terephthalate with an adsorbent to furtherreduce its yellowness index; wherein at least steps (a) and (b) areperformed substantially in the absence of oxygen.
 22. The process ofclaim 21 wherein the adsorbent is magnesium silicate.
 23. A process formaking a bis(aryloxyalkyl)terephthalate suitable for use as anantiplasticizer for polymers, comprising the steps of: (a) reactingdimethyl terephthalate with an excess of an aryloxyalkanol in thepresence of a condensation catalyst comprising zinc at a temperatureless than the boiling point of the aryloxyalkanol to produce anintermediate mixture comprising a bis(aryloxyalkyl)terephthalate, amono(aryloxyalkyl)terephthalate, and unreacted aryloxyalkanol; (b)continuing to react the intermediate mixture at a temperature within therange of 150° C. to 250° C. under reduced pressure while removingunreacted aryloxyalkanol and reducing themono(aryloxyalkyl)terephthalate content of the mixture to less than 1mole % based on the combined amounts of mono- and bis-esters; and (c)removing additional unreacted aryloxyalkanol to provide a purifiedbis(aryloxyalkyl)terephthalate having an overall purity of at least 95mole % and a yellowness index less than 10; wherein at least steps (a)and (b) are performed substantially in the absence of oxygen.
 24. Theprocess of claim 23 wherein from 1.9 to 3.0 molar equivalents of thearyloxyalkanol are used in step (a).
 25. The process of claim 23 whereinfrom 70 to 80 mole % of the dimethyl terephthalate is converted to thebis(aryloxyalkyl)terephthalate in step (a).
 26. A process for making abis(aryloxyalkyl)terephthalate suitable for use as an antiplasticizerfor polymers, comprising the steps of: (a) reacting dimethylterephthalate with an excess of an aryloxyalkanol in the presence of acondensation catalyst comprising a Group 3, 4, 12, 13, 14, or 15 metalat a temperature less than the boiling point of the aryloxyalkanol toproduce an intermediate mixture comprising abis(aryloxyalkyl)terephthalate, a mono(aryloxyalkyl)terephthalate, andunreacted aryloxyalkanol wherein from 65 to 85 mole % of the dimethylterephthalate is converted to said bis(aryloxyalkyl)terephthalate and 15to 35 mole % of the dimethyl terephthalate is converted to saidmono(aryloxyalkyl)terephthalate; (b) continuing to react theintermediate mixture at a temperature within the range of 150° C. to250° C. under reduced pressure while removing unreacted aryloxyalkanoland reducing the mono(aryloxyalkyl)terephthalate content of the mixtureto less than 1 mole % based on the combined amounts of mono- andbis-esters; and (c) removing additional unreacted aryloxyalkanol toprovide a purified bis(aryloxyalkyl)terephthalate having an overallpurity of at least 98 mole % and a yellowness index less than 10;wherein at least steps (a) and (b) are performed substantially in theabsence of oxygen.
 27. The process of claim 26 wherein from 1.9 to 3.0molar equivalents of the aryloxyalkanol are used in step (a).
 28. Theprocess of claim 26 wherein from 70 to 80 mole % of the dimethylterephthalate is converted to the bis(aryloxyalkyl)terephthalate in step(a).
 29. The process of claim 25 wherein the purifiedbis(aryloxyalkyl)terephthalate has an overall purity of at least 99 mole%.
 30. The process of claim 26 wherein the unreacted aryloxyalkanol isremoved in step (b) with a gas or vapor purge.
 31. The process of claim26 wherein step (b) is performed at a temperature within the range of175° C. to 230° C.
 32. The process of claim 26 wherein the unreactedaryloxyalkanol is removed in step (c) under reduced pressure with a gasor vapor purge.
 33. The process of claim 26 wherein the unreactedaryloxyalkanol is removed in step (c) by fractional melt or solventcrystallization.